var arr1 = [1,2,3,4,5,6,7,8,9];
var arr2 = [1,2,3,4,5];
// 第一个数组在第二个数组中不同的项
async function difference(arr1, arr2) {
  const diffArray = arr1.filter(function(v) {
    return arr2.indexOf(v) === -1;
  })
  console.log(diffArray);
}

difference(arr1, arr2);